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Full text of "The Geology of Killiney"

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376 



THE IRISH PENNY JOURNAL. 



THE GEOLOGY OF KILLINEY. 
Few cities can boast of such a variety of beautiful scenery in 
its immediate vicinity as occurs within a short distance from 
Dublin. We need not allude to the objects of deep historical 
interest Ttith which the natural beauties of Dublin are associa- 
ted, as they have often been illustrated in these pages. The 
picturesque beauties of Dublin Bay and the county of Wick- 
low are known to all ; but it is less generally known that 
the same localities abound in matters well calculated to excite 
the curiosity of the naturalist. From the great variety of 
rocks, and consequently of soil, around Dublin, we find a cor- 
responding variety in its vegetable productions ; and we believe 
we are pretty correct when we state that the botanist may 
collect specimens of nearly two-thirds of the indigenous plants 
of Ireland within the distance of a few mites from the capital. 
As regards Zoology, or the study of animals, our position is 
equally fortunate. The shores near Malahide are uncom- 
monly rich in marine productions, especially shells ; and the 
Bay of Dublin is not inferior to the coasts of Devonshire for 
the variety of its zoophytes and corallines. In the work of 
Ellis on British Corallines, we find that, although that admir- 
able naturalist resided in London, he obtained many of his 
finest specimens from Dublin. In respect to mineralogical 
and geological pursuits, we are equally well situated. At 
Killiney and in the mines of 'VVicklow several interesting and 
some very rare minerals may be collected. In geology, in 
the strict sense of the word, there are many curions pheno- 
juena which should be repeatedly examined by the student, 
and he will find such a mode of proceeding infinitely more 
profitable than the more indolent method of confining his re- 
searches to such instruction as can be found in books and 
sections. At Howth, or the promontory of Bray, he may 
examine every diversity of stratification, and may observe all 
the upheaviogs and contortions to which rocks have been ex- 
posed, displayed as in a model, open to the contemplation of 
the man of science, and to the instruction of all. The granite 
veins of Killiney are also extremely curious, and well deserve 
to be repeatedly visited by the beginnerin geological pursuits. 
It is true that the questions to which such phenomena gave 
rise have been long since sot at rest ; but it is also true 
that the questions must be mastered by every student, and w^e 
know of no place where this can be done to more advantage 
than at Killiney. 

Every one is aware that rocks are formed in two very dif- 
ferent ways . they may be produced either from the decayed 
materials of older rocks, carried down to the sea or lakes by 
the rivers, and subsequently consolidated by various processes, 
which geologists have explained, or they may be formed by 
the solidifying of liquid matter poured forth through some 
volcanic aperture from the deeper parts of the earth. The 
first kind of rocks ai'e disposed in layers, beds, or strata, by 
the return of water, and hence are called stratified, and also 
aqueous or water-formed ; the second, being liquid matters 
which have become hard from cooling, are called igneous, or 
fire-produced rocks. As volcanoes are at present confined to 
particular regions of the earth, some may imagine that such 
igneous rocks should only be found in volcanic regions. This, 
however, is a mistaken supposition, for geology assures us 
that igneous rocks are to be found in every mountain range. 
The mode of reasoning which they follow is equally simple 
and convincing. If we visit Howth, for example, we find 
many of the strata resting on their edges, or variously 
twisted. At the Killerys in the west of Ireland we find 
strata composed of rolled pebbles, elevated to a very consider- 
able angle. It is impossible that strata of loose sand or gravel 
would have been originally deposited in such inclined positions, 
and we know of no natural power which would elevate them 
but that of the igneous agency, producing either a violent 
earthquake, or a long-continued upward pressure. This 
opinion is much strengthened, when we find in every country, 
whether volcanic or not, a series of rocks which appear to 
have been violently inserted among the strata, and which we 
can prove were once in a state of intense heat and fusion, like 
the lavas from a modem volcano. 

The granite of Killiney is one of those igneous rocks, and 
the appearances which we detect in that interesting locality 
afford satisfactory evidence of its mode of formation. "When 
we descend to the shore by the stairs, a little to the east of 
the Obelisk, we find ourselves in a little way bounded by per- 
pendicular rocks. These rocks are of two kinds — granite, 
and a schistoze or slaty rock, of a bluish colour, which we 



may term mica-schist. We then observe that the mica-schist 
rests on its edges, on a pavement of granite, and also reclines 
against that rock. The junction of the tw'o rocks may be 
seen with the utmost perspicuity ; and there is no blending 
of their characters, even where they are in absolute contact. 
We may next observe a ledge of rock partly covered by the 
waves, and extending in nearly a north and south course 
along the shore. This is a granite vein of many feet is 
breadth, and several himdred yards in length, and may easily 
be traced for a considerable distance. This granite vein is 
bounded on both sides by mica-schist ; and, what is still more 
important, we may follovv' the vein till it is lost in the general 
mass of granite of the hill. When we now remember that the 
water-formed rock (the mica-schist) is standing on edge, a 
suspicion arises that the granite is a fire-produced rock, and 
has been the agent of this elevation, and the large wall of 
granite may have been intruded in a molten state between 
the beds of mica-schist. If it be objected that the granite 
vein is merely a portion of the strata of mica-schist, aud was 
like them deposited from water, an inspection will dissipate 
this illusion ; for we observe that the great vein running pa- 
rallel to the strata gives off a smaller vein at right angles 
to the direction of the strata. On examining this smaller vein, 
which may be seen a little to the north of the stairs, all doubts 
respecting its nature or origin are very soon removed. We 
are surprised to find that this vein contains fragments of the 
mica-schist. We may therefore conclude from this that 
originally fissures were produced in the schist, and these 
fissures were filled up by molten granite, which entangled 
fragments of the mica-schist which fell from the sides ot the 
fissure. It is scarcely necessary to add, that w« know of no 
agent capable of melting granite but heat. 

When we examine this interesting spot a little more mi- 
nutely, we detect many other granite veins, each affording some 
curious and minute fact in harmony with the preceding re- 
marks. Every one knows that it is easier to split a piece ot 
wood in the direction of the grain, than transversely to that 
direction. In the same way we may infer that it is easier for 
a liquid granite to insinuate itself between the strata than to 
force its way across them, and on examination we find this to 
have been the case. In the first place, the large vein first 
mentioned running in the course of the strata is broader than 
all the transverse veins put together. Secondly, when we 
examine the cross veins, we find they have had more difficulty 
in forcing their way : hence they frequently contain fragments. 
Perhaps, however, an examination at another point near the 
entrance of the abandoned lead-mine affords the most curious 
evidence of these remarks, for there we perceive that the vein 
does not hold a straight course, nor is it of equal thickness 
throughout, but, on the contrary, is of unequal breadth, and 
serpentine, as if the strata had been violently lacerated instead 
of being split. In this case the vein has cut across the strata, 
and includes fragments of the mica-schist. But the most 
curious circumstance in this example is, that the vein itself 
has been broken, and its fractured extremities a little dis- 
placed and detached, thus proving that the strata had been 
exposed to concussion and displacement at a period posterior 
to that when the vein was formed. 

If this very brief description will induce any of our readers 
to visit the granite veins of Killiney, we tire sure he will find 
that his excursion will not be an unimproving one, and he will 
perhaps be convinced that he has only to look about him to 
find sources of enjoyment which so many are ignorant of, but 
which are within the command of all. S. 



DoMBSTic Discipline of the Ddtch. — There are two 
things of a peculiar character in Holland, which deserve to be 
noticed. One is the enactment authorising husbands, wives, 
and children to be imprisoned in a house of correction set 
apart for the chastisement of offences against the laws by 
which the relations of social life are governed— the other, a 
contrivance for compelling the incorrigibly idle to work. In 
one of the rooms is a pump, and a stream of water runs in 
from the ceiling ; so that unless the prisoner labours continual- 
ly, he must be inevitably drowned. 



Printed and published very Saturday by Gonn and Cameron, at the Office 
of the General Advertiser, No. e.Church Lane, Collef e Green, Dublin.^ 
Agents: — R. Gkoombridge, Panyer Alley, Paternoster Row, London; 
SiUMS and Dinuam, Exchange Street, fllanchester ; C. Davies, North 
Jolm Street, Liverpool; John Men2IE8, Prince's Street, Edinburgh; 
and David Kobstsos, Trongate, Glasgow.